Brushhead assembly for a power toothbrush

ABSTRACT

A brushhead assembly for use with a power toothbrush, comprising a toothbrush element ( 18 ), a mounting neck ( 22 ) on which the toothbrush element is mounted and a coupling member ( 24 ) which mates a driveshaft (from a drive system in a handle assembly portion ( 12 ) of the toothbrush to the mounting neck. A ring member ( 34 ) is positioned within a groove ( 30 ) at the proximal end ( 32 ) of the coupling member to create a desired brushhead assembly inertia. On an extending portion of the coupling member is mounted a spring member ( 28 ) which is configured and arranged and has such a spring rate that when the coupling member and mounting neck are installed into a driveshaft, a preload force is created between the brushhead assembly and the driveshaft sufficient to react the torque created by the rotating inertia movement of the brushhead assembly, without lost motion or noise.

This invention relates generally to brushhead assemblies for power toothbrushes and more specifically concerns specific elements within a coupling portion of the brushhead assembly which provides improved operation of the toothbrush.

There are many types of brushhead assemblies which are currently used on power toothbrushes. These brushhead assemblies include coupling members which connect a toothbrush motor driveshaft to a support arm/neck portion of the brushhead assembly, on which is mounted a toothbrush member. The coupling member transfers torque loads between the driveshaft and the brushhead assembly, and vice versa, as the driveshaft and the brushhead rotate or oscillate through a particular angle. If the coupling member cannot react action of the driveshaft and the corresponding action of the brushhead assembly, the result is lost motion and/or noise in operation of the toothbrush.

The acceleration of the mass of the brushhead assembly in response to oscillating action of the driveshaft creates a large torque load on the driveshaft. When coupling members include plastic elastic springs to preload the brushhead assembly to the driveshaft, the forces on brushhead assemblies of certain power toothbrushes become too great for the plastic springs to withstand, given the current required small size of the brushhead assembly.

Accordingly, it is desirable to be able to reliably react the torque created by action of the driveshaft and the related acceleration of the brushhead assembly, without lost motion and/or noisy operation.

An important consideration in a power toothbrush is the tuning of the rotational inertia of the system. It is desirable that the brushhead assembly and the remainder of the toothbrush (the handle with the drive train) have an inertia ratio which produces good cleaning results. Presently, it is difficult and expensive to tune the system inertia to achieve the desired ratio with different sizes of brushheads or attachments and a common drive system/platform. It would hence be desirable to have a brushhead assembly which includes the capability of conveniently and simply adjusting, i.e. “tuning”, the inertia of a variety of brushhead assemblies to achieve a desired inertia ratio with a given drive system/handle assembly.

One aspect of the embodiments disclosed herein is directed toward a brushhead assembly for use with a power toothbrush which includes a handle assembly to which the brushhead assembly is mounted, comprising: a toothbrush member; a mounting neck member on which the toothbrush member is mounted; a coupling member which mates a motor driveshaft from a handle assembly portion of the toothbrush to the mounting neck member; and an inertia member assembly associated with the coupling member for producing a pre-selected inertia ratio between the brushhead assembly and the handle assembly.

Another aspect of the disclosed embodiments is directed toward a brushhead for use with a power toothbrush, comprising: a toothbrush member; a mounting neck on which the toothbrush member is mounted; a coupling member which mates a driveshaft from a motor drive assembly contained within a handle assembly portion of the toothbrush to the mounting neck; and a spring member fitted on an extending portion of the coupling member, into which coupling member the driveshaft fits sufficiently tightly, with the force of the spring member, to transfer the oscillating action of the driveshaft to the mounting neck, and vice versa, as the brushhead member oscillates in response to action of the driveshaft.

FIG. 1 is a partially exploded view of a toothbrush with a removable brushhead assembly.

FIG. 2 is an exploded view of the removable brushhead assembly of FIG. 1, which includes a coupling portion.

FIGS. 3A, 3B and 3C are front elevational, side elevational and rear elevational views of the coupling portion of FIG. 2.

FIG. 3D is a cross-sectional view of FIG. 3B.

FIG. 4 is a perspective view showing a coupling spring element in place on the coupling portion.

FIGS. 5A and 5B are perspective and elevational views of the coupling spring of FIG. 2.

FIG. 6 is a simplified diagram showing a nodal-mounted resonance system for a power toothbrush.

FIG. 7 is an exploded view of a coupling member showing the inertia ring relative thereto.

FIG. 8 is a cross-sectional view showing the inertia ring in place on the coupling member.

FIG. 9 is a perspective, partially cutaway view of a coupling member with the inertia ring therein.

FIG. 1 shows a power toothbrush 10, comprising generally a handle portion 12 which includes a drive assembly which oscillates a driveshaft 14 through a specific angle. In one example, the angle is ±8° for a total of brushhead movement of 16°. Other angles of movement may be used. Mounted on an end portion 15 of driveshaft 14 is a brushhead assembly 16. Brushhead assembly 16 includes a toothbrush member 18, a mounting arm or neck 22 and a coupling member 24.

Referring to FIG. 2, mounted on the distal end 26 of coupling member 24 is a coupling spring 28. Coupling member 24 connects, i.e. couples, the driveshaft 14 to mounting arm 22. Mounted in a circular groove 30 in the proximal end 32 of coupling member 24 is an inertia ring 34. Mounted on the proximal end 32 of coupling member 24 is a color ring 38 which abuts handle portion 12 when the brushhead assembly is operatively positioned on the handle portion.

Disclosed herein is inertia ring 34 which is used to create a desired inertia ratio between brushhead assembly 16 and the remainder (the handle with the drive train) of the toothbrush. Also disclosed herein is coupling spring 28 which mates coupling member 24 to the driveshaft 14 for reliably transferring drive torque from driveshaft 14 to the brushhead assembly 16 and for reacting torque from the accelerating brushhead assembly 16 back to the driveshaft 14 without a loss of torque/motion or vibration.

FIGS. 3A, 3B, 3C and 3D show coupling member 24 in more detail. Coupling member 24 in the embodiment shown is plastic. It has a color ring groove 42 at the proximal end exterior surface for locating and retaining color ring 38. This arrangement permits ease of user installation and removal of color ring 38; different color rings are used to identify different users.

Forward of groove 42, the coupling member 24 has an inwardly angled surface portion 43, i.e. cone-shaped, with a length of approximately ¼ inch, until a lower radial locating ring 44 is reached. Locating ring 44 is used to adjust the fit of the coupling member 24 and to positively locate the coupling member to the lower edge 27 of mounting neck 22.

Extending forwardly from the radial locating ring 44 is a brushhead assembly axial retention portion, comprising two opposing recesses 46 and 48. These are configured to mate with matching portions on the interior surface of mounting neck 22, and provide the retention capability to maintain coupling member 24 in mounting neck 22 during operation. Extending between the end of angled surface portion 43 to the distal end 26 of coupling member 24, located peripherally around the mounting member half-way angularly between recesses 46 and 48, is a torque transfer rib 52. Rib 52 is approximately ⅛-inch wide and ½-inch long. Rib 52 interfaces with a mating recess in mounting neck 22 and acts as a primary element for transfer of torque between driveshaft 14 and mounting neck 22.

Positioned 180° from rib 52 is a preload contact element 56. As discussed in more detail below, element 56 acts to take up the clearance between coupling spring 28 and driveshaft 14, and transfers the preload force of spring 28 into a clamping action on the driveshaft, to provide torque transfer. An alignment rib 60 is aligned with contact element 56, positioned between angled surface portion 43 and the proximal end of contact element 56. The alignment rib 60, along with rib 52, acts to transfer torque between coupling member 24 and mounting neck 22, as well as minimizing angular motion between these two members.

Coupling member 24 includes a cap element 58 at the distal end 26 of coupling member 24. The cap 58, along with ring 44, transfers user-generated loads on the brushhead from mounting neck 22 to coupling member 24, as well as reinforces and provides additional stiffness to the distal end surface of coupling member 24.

Referring now to FIG. 3D, the coupling member 24 at its proximal end 32 thereof includes a circular groove 70 which extends into the coupling member, the groove including a swage lip 72 at the rear outer peripheral edge thereof. The inertia ring 34 (not shown) fits within groove 70. Groove 70 locates and restrains the inertia ring 34. Three crushable ribs 74 are spaced around the outer peripheral surface of groove 70 to adjust and maintain the fit and tolerances between inertia ring 34 and groove 70, assisting in preventing rotational slippage of the inertia ring 34 relative to the coupling member 24 during operation of the appliance. This will be described in more detail below.

FIG. 4 and FIGS. 5A and 5B show the coupling spring member 28 in more detail, including in its operative position around the distal end of coupling member 24 within driveshaft 14 in place within coupling member 24. In the embodiment shown, spring 28 is made from metal and is formed into a generally angular “C” shape, that fits around the distal end portion 26 of the coupling member. The “C” shape spring member 28 is 5.0 mm in dimension 57 and 3.55 mm in dimension 59, with an opening 61 of 1.7 mm. Spring member 28 is made from stainless steel, approximately 0.15 mm thick.

When operatively positioned, it is in contact with transfer rib portion 56, which is pushed slightly outwardly by the insertion of driveshaft 14. The C-shaped spring member 28 extends around the distal end portion of the coupling member, with the longitudinal edges of the opening contacting alignment rib 52.

Spring 28 is arranged so that the torque provided by driveshaft 14 through coupling 24 is transferred to the mounting neck 22; the arrangement also reacts the torque produced by acceleration of the brushhead assembly back to the driveshaft. A minimum force F_(min) is required to stop the spring 28 from opening and causing lost motion in the system. The force designated F in FIG. 4 is created against the spring member, when operatively positioned, to allow tolerances in the parts. The force F must be great enough to maintain good torque transfer, without slippage, while not being so great as to make the force necessary for axial removal of the combination of the mounting neck and brush element mounted thereon from the coupling member inconvenient for the average user.

The force F is created by deforming the spring member 28, which has a stiffness K. The important parameters of the spring are the maximum spring deflection, the minimum preload force and the maximum preload force. The minimum preload force F_(min) discussed below is defined by the torque transfer requirement between the driveshaft 14 and the brushhead assembly 16. The maximum force F_(max) is determined by the maximum displacement of the spring and the spring rate. Spring rate deflection is based on the clearances between the coupling member 24 and the mating surfaces of the driveshaft. The minimum preload force is F_(min)=T_(max)/d, where T_(max) is equal to the maximum torque on the device, and d is equal to the distance 73 in FIG. 4. In one example, T_(max) is 50.2 Newton-mm, while d=1.47 mm, and F_(min) is 34.15N.

The spring rate K can be calculated as follows:

$K = \frac{F_{\min}}{i_{\min}}$

where i_(min) equals i_(nominal)-tolerance value. i_(nominal) equals 0.5 mm, while tolerance value equals ±0.17 mm; i_(min) thus equals 0.5−0.17=0.33 mm. From above, where F_(min) equals 34.15 N in order to provide the desired torque transfer, K equals 103.5 N/mm. The maximum spring force now can be calculated. Using the above spring rate and the interference tolerance, the maximum spring force is 69.4 N.

In actual use, spring 28 opens after insertion of the coupling member into the mounting neck until it contacts the internal surface of the mounting neck 22, thereby engaging the coupling member 24 with the mounting neck 22. With such an arrangement, points 78 and 80 (FIG. 4) between driveshaft 14 and the coupling member 24 do not rock or open as the driveshaft 14 oscillates in operation.

Hence, in functional summary, coupling spring 28 deforms slightly as the driveshaft 14 is inserted into the coupling member 24, thereby creating a preload that is sufficient to react the dynamic torque between the driveshaft and the coupling neck without lost motion or noise.

Further, the spring rate discussed above, with the stated minimum and maximum spring forces, results in a convenient pull-off force for the mounting neck. The coupling spring 28 produces a sufficiently high preload, in a small size, that smaller components can be used for the toothbrush, which is desirable.

There are alternatives to the specific angular C-shaped configuration of FIGS. 5A and 5B. The spring could be a closed oval, or a closed circle. Further, the spring could be a coil spring, while in still another alternative, a leaf spring is attached to the coupling member, extending more or less parallel to the axis of the shaft. The spring deforms when the shaft is inserted and provides a preload to react torque back to the shaft from the acceleration of the rotating mass. The leaf spring could be attached to the mounting neck instead of the coupling.

The inertia ring 34, as indicated above, fits into the circular groove 70 in the proximal end 32 of the coupling member 24, as shown most clearly in FIGS. 7 and 8. While the ring 34 is preferably made from metal, it can also be made from various ceramics, plastic or wire, although the material should preferably have a higher density than the other components of the brushhead assembly. The significance of the ring is illustrated in FIG. 6, which is a schematic illustration of a nodal-mounted resonance system 86 for a power toothbrush. It should be understood, however, that the inertia ring is not limited to a nodal system. The inertia ring creates a desired ratio between both sides of the node in a nodal system. The nodal resonance system 86 includes two counter-rotating masses 88 and 90 and a central nodal mount 92 which remains still while masses 88 and 90 counter-rotate. Spring members 89 and 91 connect the masses to the nodal mount. The nodal mount 92 is connected to the housing (handle) 94 by spring 95.

The counter-rotating masses have specific values of rotational inertia, such that a given rotational excitation input results in a given rotational output, with the system operating at a resonant frequency. The inertia ring provides an ability to easily produce the desired inertia ratio between the input system 88 and the output system 90. The inertia ring positioned in the proximal end of the coupling member, when properly selected, produces a desired inertia ratio between the brushhead assembly and the handle/drive system assembly. The size, configuration and material of the ring can be adjusted so that the resulting inertia of the brushhead portion of the system is such as to produce the desired inertia ratio between the brushhead portion and the handle portion of the system. For instance, in a given toothbrush, it may be desirable to change the brushhead with a different inertia. The inertia ring is then designed to produce the desired ratio between the brushhead and handle portions. The ratio can vary. One example of an inertia ratio which produces good cleaning results is 1.5. The design of the inertia ring is carried out as follows.

The brushhead system will have a specific inertia value, i.e. the rotational inertia of the brushhead about the axis of rotation 80 (FIG. 7). The difference between the required brushhead inertia to provide the desired ratio and the sum of the actual calculated inertia of the various brushhead assembly components must be made up by the inertia ring. An example of an inertia ring is shown in FIGS. 7 and 8, which includes inertia ring 34 positionable in coupling member 24, at the distal end of which is the coupling spring 28. When ring 34 is in an operative position, it is contained within circular groove 70, as shown in FIG. 8. In one specific embodiment, the ring is made from metal, such as stainless steel, with an outside diameter of 12.2 mm, a thickness of 1.0 mm and a width of 3.30 mm. The peripheral edges of the ring are typically chamfered.

A ring configuration is most convenient to accomplish the matching inertia function, since it has inherently the important characteristic of being symmetrical about the rotational axis of the appliance when it is located within groove 70. However, while ring 34 is shown as a single member, it could be a plurality of separate elements, such as arcuate segments, as long as the segments in combination are symmetrical in position about the rotational axis of the appliance. It is possible for the inertia member to be asymmetrical if correctly compensated for. Also, while preferably the ring is within the coupling member, it could be positioned outside the coupling member.

It is important that the inertia ring be held firmly within the groove, as if it were rigidly attached to the driveshaft. Any movement of the ring within groove 70 must thus be prevented, axially as well as rotationally. Axial movement is prevented by the crushable ribs 74 present in groove 70, which tend to hold the ring against axial movement. Rotational movement is prevented by frictional contact between the outer surface of the ring and the matching groove surface.

There is a maximum torque which can be tolerated by the combination before slippage of the ring occurs. The maximum torque T=r*F_(f)=r·UF_(N), where r is the distance between the exterior surface of the ring and the axis of the coupling member, U is the coefficient of friction between the exterior surface of the ring and the surface of the coupling member groove and F_(N) is equal to the normal force exerted against the ring toward the axis. The friction force (i.e. the coefficient of friction U, multiplied by the normal force F_(N)) must be large enough to prevent slippage of the ring within the groove 70, which would lead to noise and an inefficient transfer of torque between the brushhead assembly and the driveshaft. With a known radius, coefficient of friction and normal force, the maximum torque which can be placed on the coupling member can be readily calculated.

Hence, a coupling spring and an inertia ring have been disclosed which increase the operating effectiveness of brushhead assembly action in a power toothbrush which includes a driveshaft extending from the handle portion thereof. The inertia ring is used in a nodal-mounted dynamic resonance system.

Although a preferred embodiment of the invention has been disclosed here for the purposes of illustration, it should be understood that various changes, modifications and substitutions may be incorporated in the embodiment without departing from the spirit of the invention, which is defined by the claims which follow. 

1. A brushhead assembly for use with a power toothbrush which includes a handle assembly to which the brushhead assembly is mounted, comprising: a toothbrush member (18); a mounting neck member (22) on which the toothbrush member is mounted; a coupling member (24) which mates a motor driveshaft (14) from a handle assembly portion (12) of the toothbrush to the mounting neck member; and an inertia member assembly (34) associated with the coupling member for producing a pre-selected inertia ratio between the brushhead assembly and the handle assembly of the toothbrush.
 2. The brushhead assembly of claim 1, wherein the inertia member assembly is positioned so as to be symmetrical about a rotational axis of the toothbrush.
 3. The brushhead assembly of claim 1, wherein the inertia member assembly is positionable within the coupling member.
 4. The brushhead assembly of claim 1, wherein the inertia member is positionable on the outside of the coupling member.
 5. The brushhead assembly of claim 1, wherein the inertia assembly is a continuous ring.
 6. The brushhead assembly of claim 1, wherein the ring is metal.
 7. The brushhead assembly of claim 5, wherein the ring has a dimension which is greater than the other parts of the brushhead assembly.
 8. The brushhead assembly of claim 5, wherein the ring is a ceramic or plastic material.
 9. The brushhead assembly of claim 1, wherein the inertia assembly is positioned in a circumferential groove (30) at a proximal end (32) of the coupling member.
 10. The brushhead assembly of claim 5, wherein the friction force between the inertia ring and the coupling member is sufficient to prevent rotational slippage of the ring at torque values encountered during normal operation of the toothbrush.
 11. The system of claim 9, wherein the circumferential groove includes elements (74) tending to prevent axial and/or rotational movement of the ring during operation of the toothbrush.
 12. In a brushhead assembly for use in a power toothbrush which comprises a toothbrush member (18), a mounting neck element (22) on which the toothbrush member is mounted and a coupling member (24) which mates a motor driveshaft (14) from a motor drive assembly present in a handle assembly portion (12) of the power toothbrush to the mounting neck, the improvement comprising: a ring member (34) connected to the coupling member for tuning the inertia of the brushhead assembly relative to the inertia of the handle assembly portion of the toothbrush to a pre-selected ratio.
 13. The improvement of claim 12, wherein the ring member is positioned within a circumferential groove (30) in the coupling member so that it is symmetrical about the rotational axis of the toothbrush.
 14. The improvement of claim 12, wherein the ring member is metal, and, wherein the friction force between the ring member and the groove in the coupling member is such as to substantially prevent rotational slippage of the ring member at values of torque on the coupling member produced during operation of the toothbrush.
 15. A brushhead for use with a power toothbrush, comprising: a toothbrush member (18); a mounting neck (22) on which the toothbrush element is mounted; a coupling member (24) which mates a driveshaft (14) from a motor drive assembly contained within a handle assembly portion (12) of the toothbrush to the mounting neck; and a spring member (28) fitted on an extending portion of the coupling member, into which coupling member the driveshaft fits sufficiently tightly, with the force of the spring member, to transfer the oscillating action of the driveshaft to the mounting neck, and vice versa, as the brushhead member oscillates in response to action of the driveshaft.
 16. The brushhead assembly of claim 15, wherein the spring member is insertable onto and removable from the extending portion of the coupling member and wherein the spring member is configured and arranged structurally to produce a sufficiently tight fit between the spring member, coupling member and the driveshaft to react and/or transfer torque between the driveshaft and the brushhead assembly when the driveshaft is operatively inserted into the coupling member and the coupling member is operatively inserted into the mounting neck.
 17. The brushhead assembly of claim 15, wherein the spring member produces a preload which is sufficient to prevent relative movement between the brushhead member and the driveshaft while permitting convenient removal of the mounting neck and brush element from the driveshaft.
 18. The brushhead assembly of claim 15, wherein the spring member is an angular C shape which fits around the exterior surface of the coupling member.
 19. The brushhead assembly of claim 15, wherein the spring member is in the form of a closed oval, a closed circle, a coil spring or a leaf spring.
 20. In a brushhead assembly for use with a power toothbrush which comprises a toothbrush element (18), a mounting neck (22) on which the toothbrush element is mounted and a coupling member (24) which mates a driveshaft (14) from a motor drive assembly within a handle assembly portion (12) of the toothbrush to the mounting neck, the improvement comprising: a spring member (28) fittable onto an extending portion of the coupling member (24), into which coupling member the driveshaft fits sufficiently tightly, with the force produced by the spring member, that the coupling member follows the oscillating action of the driveshaft and reacts the torque from the resulting oscillating action of the brushhead assembly.
 21. In the brushhead assembly of claim 20, the spring member comprises a metal element, with a spring rate which prevents lost motion between the driveshaft and the mounting neck. 